Pumps are used to pump fluids, including liquids and gasses, and to compress gasses. These devices may be powered by engines or motors that supply rotary motion, which may be converted to a reciprocating motion in some cases. Generally, rotary pumps and compressors may be more efficient since the direction of motion is not changed, as is the case with reciprocating engines. However, there continues to be a need for improved rotary pumps and compressors.